We often hear about iron deficiency anemia. We hear much less about latent iron deficiency. What is the difference between those two iron deficiency forms?
Iron deficiency anemia is a situation, where hemoglobin level and often also hematocrit and red blood indeces have decreased in value. In case of latent iron deficiency, blood test is still between reference values (however, often values have decreased), but iron stores, i.e. ferritin level, is low.
How empty should iron stores be for latent iron deficiency diagnosis?
International studies have found that ferritin level less than 30 is the reference value for latent iron deficiency diagnosis. Such value is also used e.g. in many places in Finland  . In Estonia, medical stuff should also follow the same instructions, but everything depends on the doctor and his or her knowledge about latent iron deficiency. Often laboratory´s reference values are strictly followed, whereas the lower reference value in Estonia for adult women is only 10 . In such cases, people with iron deficiency symptoms suffering from latent iron deficiency are left without attention , not to mention those people, who do not have symptoms.
Do we always have symptoms in case of latent iron deficiency?
Everything depends on a person – we all tolerate iron deficiency a bit differently. There are people, who have symptoms with ferritin values less than 30 and even above, but there are also people, whose ferritin value is very low without any symptoms. This makes latent iron deficiency extremely sneaky – without knowing a person´s ferritin level, it is not possible to correctly evaluate his or her iron stores. Ferritin test is one of the most important analysis in diagnosing iron deficiency .
A 2018 study, where hematological parameters of children from different age groups were measured, analyzed the reference value lower limits of ferritin values, when children´s hematological parameters did not change anymore or improve. That study suggested taking into account the following ferritin values for children for latent iron deficiency diagnosis: 4 months – 13 years 26 μg/l and 13–19 years (incl.) 39 μg/l.
Dr Neve Vendt and dr Heli Grünberg from The Children’s Clinic of Tartu University Hospital carried out a research about Estonian 9–12 months infants suffering from latent iron deficiency and iron deficiency anemia. Also doctors from Tartu University Clinic brought out the importance that hemoglobin measurements are not enough for diagnosing iron deficiency. In order to prevent iron deficiency anemia, it is important to correctly diagnose latent iron deficiency .
Is latent iron deficiency harmful? What happens in our bodies in case of latent iron deficiency?
- international research has found that brain suffers from iron deficiency, when ferritin level decreases below 35 μg/l -> harmful neurological effect, brain development disorders 
- children with low iron stores suffer more often from learning difficulties and difficulty concentrating, cognitive and motor development disorders 
- adults as well as children suffer from decrease in physical endurance and working capacity 
Dr Vendt and Dr Grünberg from Estonia also brought out that in case of latent iron deficiency, our bodies suffer from brain, blood and muscular physiological disorders . When latent iron deficiency has already developed and iron deficiency is not paid attention to, brain can suffer from irreversible neurological damage in terms of behavioral deficiencies that are not possible anymore to fix with iron treatment . Therefore latent iron deficiency is extremely harmful for infants and children, whose brain is still developing. Iron treatment in case of correctly diagnosed iron deficiency is very important, but even more important is prevention of latent iron deficiency to prevent irreversible damage to children´s brain development and iron deficiency anemia. The most critical time for infants and toddlers are the first 1000 days, where brain develops at a very fast speed .
Risk groups of latent iron deficiency?
- growing children, mainly aged 6–24 months: increased need for iron during growing phases is one of the risk factors for iron deficiency. Iron from food does not compensate the increased iron need in those periods. Read more about iron deficiency among toddlers from HERE.
- infants with birth weight below 3 kg and premature babies -> low iron stores already when born
- women in fertile age: iron exits the body mainly through blood. Women in fertile age are in the risk group due to menstruation. In case of normal menstruation, women lose approximately 25–45 ml of blood and the upper limit for blood loss is around 80 ml. Heavy menstruation is with blood loss more than 80 ml . 1 ml of blood = 0,5 mg of iron, therefore, 30 ml blood loss means 15 mg of iron loss. In order to compensate that amount within 3–4 weeks (before new menstruation begins), we should eat 1,5 kg of red meat and here we have just taken into account 30 ml blood loss. A lot of women suffer from much heavier blood loss than 30 ml. Often the cause is not small amount of iron from food, but negative iron balance during menstruation. It is not possible to treat iron deficiency (anemia) with food! We have written more about menstruation and iron from HERE.
- pregnant women: increased need for iron during pregnancy is also one of the risk factors. Iron from food does not compensate the increased need during pregnancy and World Health Organisation (WHO) recommends 30–60 mg of iron daily from the beginning until the end of pregnancy . Read more about pregnancy and iron deficiency from HERE.
- elderly: an unbalanced diet and chronic diseases are the risk factor for iron deficiency. Chronic and infectious diseases weaker iron absorption. This is related to a hormone called hepsidin, which we discussed HERE. Elderly also suffer often from intestinal blood loss.
- vegans and vegetarians: vegans and vegetarians are in the risk groups, when diet is unbalanced and heme-iron is not compensated with good non-heme-iron sources such as whole grain products, legumes, nuts, seeds, dried fruit, buckwheat. The absorption of heme-iron is around 25% and 10% for non-heme-iron, but non-heme-iron sources contain often many times more elemental iron per 100 g compared to meat. Non-heme-iron sources also contain vitamin C, which promotes iron absorption. Thus, we should not underestimate the importance of non-heme-iron in our diets . We have written about non-heme and heme-iron HERE.
- people consuming a lot of dairy: dairy and dairy products contain a lot of calcium and a protein called casein. Calcium and casein both weaken iron absorption. Read more about cow-milk anemia from HERE.
 F. Ebeling et al. Raudanpuute ilman anemiaa – miten ferritiiniarvoa tulkitaan? Lääkärilehti 8/2019. Goodnough LT, Nemet E. Iron deficiency and related disorders. Kirjassa: Greer JP, Arber DA, Glader BE, List AF, Means RT, Rodgers GM, toim. Wintrobe’s Clinical Hematology, 14. painos. Wolters Kluwer Health 2018;615–43. Synlab Eesti. Ferritiin. Cusick SE, Georgieff MK, Rao R. Approaches for Reducing the Risk of Early-Life Iron Deficiency-Induced Brain Dysfunction in Children. Nutrients. 2018;10(2):227. Published 2018 Feb 17. N. Vendt ja H. Grünberg. Kuidas diagnoosida ja ennetada rauapuudust imikutel? Eesti Arst 2009. 88(7−8):481−484. Arcanjo FP, Arcanjo CP, Santos PR. Schoolchildren with Learning Difficulties Have Low Iron Status and High Anemia Prevalence. J Nutr Metab. 2016;2016:7357136. Günekoloog Ivi Saar – Valvekliinik. WHO. Daily iron and folic acid supplementation during pregnancy. ] A. Aro, M. Mutanen, M. Uusitupa. Ravitsemustiede, 4.–7.volume, 2017.